Various methods and devices are proposed to implement character recognition using a multi-valued digital image; in general, a binary image is a recognition object in character recognition device; a multi-valued image needs to be binarized for input. A recognition performance of the character recognition device is determined by how precisely characters, which are recognition objects, are separated from a background which is a non-recognition-object. Therefore, as a method for determining a binary threshold to binarize a multi-valued image, a character recognition device using a discriminant analysis method has been proposed/presented, for example (Patent reference 1, for example).